Water base pigment ink composition for inner lead type writing instrument

ABSTRACT

A water base pigment ink composition for inner lead type writing instruments do not comprise white colored inorganic pigments or white colored resin particles as coloring materials and the content of pigment is 0.5 to 7 wt %, the content of water-soluble resin is 2 to 10 wt % with respect to the total amount of the ink, and the viscosity is 3.5 to 10 mPa·s.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to a water base pigment ink compositionfor inner lead type writing instruments. More specifically, the presentinvention relates to a water base pigment ink composition for inner leadtype writing instruments in which written marks have pastel tones onwhite paper and which is free from such trouble as ink leakage, shadingof written marks, and the like.

Conventionally, as a pastel toned water base pigment ink composition forwriting instruments, disclosures in Japanese Patent Kokoku publicationNo. 08-009703 (Patent document 1) and Japanese Patent Kokoku publicationNo. 08-009704 (Patent document 2)are publicly known. Such a pastel tonedwater base pigment ink composition for writing instruments uses whitecolored inorganic pigments such as titanium dioxide or white coloredresin particles in order to develop pastel tones (to make written marksopaque).

However, in said conventional pastel toned water base pigment inkcomposition for writing instruments, when used for inner lead typewriting instruments, dispersion stability with time within an inner leadwas low and ink dischargeability from a pen tip was not good since saidwhite colored inorganic pigments or white resin particles settle out.

Therefore, the object of the present invention is to provide a waterbase pigment ink composition for writing instruments capable ofovercoming drawbacks of poor dispersion stability with time and inkdischargeability and with pastel toned written marks.

SUMMARY OF THE INVENTION

The present invention relates to a water base pigment ink compositionfor inner lead type writing instruments comprising no white coloredinorganic pigments or white colored resin particles as coloringmaterials, wherein pigments are contained in 0.5 to 7 wt %, watersoluble resin is contained in 2 to 10 wt %, and viscosity is 3.5 to 10mPa·s. By this composition, when such an ink is contained in a innerlead of writing instruments, pastel toned written marks can be obtained,and at the same time, ink droplet does not occur at a pen tip and thereis an effect that dispersion stability of the ink within an inner leadis good.

In addition, the viscosity in the present invention is measured using anELD viscometer 3° 14′ cone rotor with a rotation speed of 50 rpm at atemperature of 20° C.

Further, by preparing a water base pigment ink composition for innerlead type writing instruments as set forth in claim 1, in which pigmentsother than said white colored inorganic pigments or said white coloredresin particles are selected one or more species from quinacridone red,DPP red, phthalocyanine blue, phthalocyanine green, azo yellow, anddisazo yellow, an effect of good light resistance can be obtained.Further, by preparing a water base pigment ink composition for innerlead type writing instruments as set forth in claim 1 or 2, in whichsaid water soluble resins are selected one or more species from acrylicacid resins, styrene-acrylic acid resins, and styrene-maleic acidresins, the inventors have found the effects of improved dispersionstability.

In other words, in a water base pigment ink composition for inner leadtype writing instruments, by not including white colored inorganicpigments or white colored resin particles as coloring materials and bysetting the content of pigments other than white colored inorganicpigments or said white colored resin particles 0.5 to 7 wt % withrespect to the total ink, pastel tone can be obtained. However, whenwater soluble resins are contained in less than 2 wt %, the inkviscosity becomes around 2mPa·s, leaving a problem of ink droplet andpoor dispersion stability. Thus, by increasing the content of said watersoluble resins to 2 to 10 wt % compared with conventional content and byadjusting ink viscosity to 3.5 to 10 mPa·s, the above mentioned problemhas been solved.

Further, in the present invention, it is preferable to include at leastone species selected from quinacridone red, DPP red, phthalocyanineblue, phthalocyanine green, azo yellow, and disazo yellow as coloringmaterials.

Particularly, in the present invention, it is preferable to include atleast one species selected from quinacridone red, DPP red,phthalocyanine blue, phthalocyanine green, azo yellow, and disazo yellowas coloring materials in at least 0.1 to 7 wt % with respect to thetotal amount of the composition. Further, it is preferable that watersoluble resins are selected one or more species selected from acrylicacid resins, styrene-acrylic acid resins, and styrene-maleic acidresins.

DESCRIPTION OF THE PREFERRED EMBODIMENT

A water base pigment ink composition for inner lead type writinginstruments of the present invention comprises no white coloredinorganic pigments or white colored resin particles as coloringmaterials, wherein pigments other than white colored inorganic pigmentsor white colored resin particles are contained in 0.5 to 7 wt %, watersoluble resin is contained in 2 to 10 wt %, and the viscosity is 3.5 to10 mPa·s, and by preparing such a composition, dispersion stability withtime and pastel tone can be obtained.

As coloring materials used in the present invention, general organicpigments can be used and as azo pigments, such pigments as mono azopigments (β-naphthol series, naphthol AS series, acetoacetic arylamideseries, pyrazolone acetoacetic arylamide series, acetoacetanilideseries, hanzayellow series, fast yellow series), disazo series (exceptcondensation azo pigments) (acetoacetic arylamide series, pyrazoloneseries), azo rake (soluble azo pigments) (β-naphthol series,β-oxynaphthoic acid series) (BON acid series), naphthol AS series,acetoacetic allylide series), further, condensation azo pigments,chelate azo pigments, and as polycyclic pigments, such pigments asphthalocyanine series, anthraquinone series (surene series)(vat dyeseries, chelate series), perylene series, perynon series, indigo series,thioindigo series, quinacridone series, dioxadine series, isoindolinoneseries, quinophthalone series, metal complex pigments (nitro-type Nicomplex, azomethine-type Cu complex, azo-type Ni complex) methine *azomethine can be used and in view of light resistance, pigments such asquinacridone red, DPP red, phthalocyanine blue, phthalocyanine green,azo yellow, and disazo yellow are preferable. In addition, thesecoloring materials can be used alone or in combinations of two or moreof them.

These pigments can be contained in 0.5 to 7 wt %, and preferably, in 1to 5 wt %. When these pigments are contained in less than 0.5 wt %,written marks get thin, and when these pigments are contained greaterthan 7 wt %, pastel colored tone cannot be obtained. In addition, whenat least one species is used among quinacridone red, DPP red,phthalocyanine blue, phthalocyanine green, azo yellow, and disazoyellow, pigments other than these may be used together, however, in suchcases, quinacridone red, DPP red, phthalocyanine blue, phthalocyaninegreen, azo yellow, and disazo yellow can preferably be used in an amountof 0.1 to 7 wt % from the view point of light resistance and writingcharacteristics. More preferable content range is 1 to 5 wt %.

As water-soluble resins used in the present invention, water-solubleresins used for aqueous writing instruments can be used andspecifically, acrylic resins, styrene-acrylic resins, styrene-maleicresins and the like are exemplified. The content of water-soluble resincan be 2 to 10 wt % with respect to the total amount of the compositionand preferably, 2 to 5 wt %. When the content is less than 2 wt %,viscosity lowers and cause ink droplet or dispersion stabilitydeteriorates. On the other hand, when the content exceeds 10 wt %,viscosity becomes so high that ink dischargeability deteriorates.

As solvents, water is used. The content is usually 40 to 60 wt %. Whenthe content of water is less than 40 wt %, ink viscosity becomes so highthat ink dischargeability deteriorates. On the other hand, when thecontent exceeds 60 wt %, written marks get hard to dry.

In the present invention, water-soluble organic solvents can be used aswetting agents. When water-soluble organic solvents are used, as suchwater-soluble organic solvents, glycerin, ethylene glycol, diethyleneglycol, propylene glycol, and the like can be used. The content of thesewater-soluble organic solvents is preferably 10 to 30 wt %. When thecontent is less than 10 wt %, wetting effect is not satisfactory andthin spots appear in written marks, and on the other hand, when thecontent exceeds 30 wt %, written marks get hard to dry and waterresistance weakens.

Further, the present invention, surfactants may be used. As surfactants,anionic surfactants (carboxylic acid-type, sulfuric ester-type,sulfone-type, phosphoric ester-type), nonionic surfactants (ether-type,ester-type, amino ether-type, alkyl amide-type), and as for others,fluorinated-type surfactants, silicone-type surfactants, and reactivitysurfactants can be used. There surfactants can be used alone or incombinations of two or more of them. The content of these surfactants ispreferably not greater than 5 wt %, and further preferably, 0.05 to 3 wt%. When the content exceeds 5 wt %, dispersion stability of inkcompositions is inhibited.

Further, for the purpose of improving cap-off performance (prevention ofdried pen tips), urea and derivatives thereof, sugar and sugar ester andthe like may be added.

Further, as required, pH regulators, anti-rusting agents, antisepticmildew-proofing agents, and the like can be appropriately used. As pHregulators, caustic soda, ammonium, and the like can be used. Asanti-rusting agents and antiseptic mildew-proofing agents, publiclyknown ones can be used.

Ink viscosity is required to be set in the range of 3.5 to 10 mPa·s.When said viscosity is less than 3.5 mPa·s, pigment dispersion stabilitydeteriorates and such problems occur such as ink droplets, shading inwritten marks, ink leakage, and the like. On the other hand, when saidviscosity exceeds 10 mPa·s, ink dischargeability deteriorates. Methodsof regulating ink viscosity include adjusting the content of pigments,water-soluble resins, water-soluble organic solvents and also, adjustingviscosity by using additives such as surfactants and the like.

Hereinafter, the present invention is further explained in more detail.For information, the protection range of the present invention is notlimited to thee range of these Examples. In addition, ink viscosity inExamples and Comparative Examples was measured by using an ELDviscometer. Ink viscosity was measured under the condition of using a 3°14′ cone rotor, with a rotational speed of 50 rpm at a temperature of20° C. as mentioned above.

EXAMPLES Example 1

Inks with compositions shown in Table 1 were prepared respectively.

First, 25 parts by weight of azo yellow pigments, 20 parts by weight ofethylene glycol, 2 parts by weight of butylceilsolve, and 28 parts byweight of water were added to 25 parts by weight of water soluble resinliquid (20 wt % of styrene-acrylic acid resin, 2 wt % of caustic soda,and 78 wt % of water), followed by dispersing by a publicly known beadmill and further adding 32 parts by weight of water so that pigmentsconcentration gets 17 wt % with respect to the total amount of theaqueous pigment dispersion A, thereby obtaining aqueous pigmentdispersion A.

Next, to this water base pigment dispersion A, with the content shown inTable 1, 27 parts by weight of glycerin, 10 parts by weight of urea,28.8 parts by weight of water, 0.1 parts by weight of COATSIDE H(manufactured by Takeda Pharmaceutical company limited), 0.1 parts byweight of PROXEL XL-2 (manufactured by Avecia K.K.) as antisepticmildew-proofing agents, and 5 parts by weight of said water-solubleresin liquid (20 wt % of styrene-acrylic acid resin, 2 wt % of causticsoda, and 78 wt % of water) were added, thereby obtaining a water basepigment ink.

Example 2

Inks with compositions shown in Table 1 were prepared respectively.

First, 25 parts by weight of quinacridone red pigments, 20 parts byweight of ethylene glycol, 2 parts by weight of butylcellsolve, and 28parts by weight of water were added to 25 parts by weight ofwater-soluble resin liquid (20 wt % of styrene-acrylic acid resin, 2 wt% of caustic soda, and 78 wt % of water), followed by dispersing by apublicly known bead mill and further adding 32 parts by weight of waterso that pigments concentration gets 17 wt %, thereby obtaining waterbase pigment dispersion B.

Next, to this water base pigment dispersion B, with the content shown inTable 1, 28 parts by weight of glycerin, 10 parts by weight of urea,41.5 parts by weight of water, 0.1 parts by weight of COATSIDE H, 0.1parts by weight of PROXEL XL-2 and 15 parts by weight of saidwater-soluble resin liquid (20 wt % of styrene-acrylic acid resin, 2 wt% of caustic soda, and 78 wt % of water) were added, thereby obtaining awater base pigment ink.

Example 3

Inks with compositions shown in Table 1 were prepared respectively.

First, 25 parts by weight of DPP red pigments, 20 parts by weight ofethylene glycol, 2 parts by weight of butylceilsolve, and 28 parts byweight of water were added to 25 parts by weight of water soluble resinliquid (20 wt % of styrene-acrylic acid resin, 2 wt % of caustic soda,and 78 wt % of water), followed by dispersing by a publicly known beadmill and further. adding 32 parts by weight of water so that pigmentsconcentration gets 17 wt %, thereby obtaining water base pigmentdispersion C.

Next, to this water base pigment dispersion C, with the content shown inTable 1, 25 parts by weight of glycerin, 10 parts by weight of urea,41.0 parts by weight of water, 0.1 parts by weight of COATSIDE H, 0.1parts by weight of PROXEL XL-2 and 15 parts by weight of saidwater-soluble resin liquid (20 wt % of styrene-acrylic acid resin, 2 wt% of caustic soda, and 78 wt % of water) were added, thereby obtaining awater base pigment ink.

Example 4

Inks with compositions shown in Table 1 were prepared respectively.

First, 25 parts by weight of phthalocyanine green pigments, 20 parts byweight of ethylene glycol, 2 parts by weight of butylcellsolve, and 28parts by weight of water were added to 25 parts by weight of watersoluble resin liquid (20 wt % of styrene-acrylic acid resin, 2 wt % ofcaustic soda, and 78 wt % of water), followed by dispersing by apublicly known bead mill and further adding 32 parts by weight of waterso that pigments concentration gets 17 wt %, thereby obtaining waterbase pigment dispersion D.

Next, to this water base pigment dispersion D, with the content shown inTable 1, 25 parts by weight of glycerin, 10 parts by weight of urea,41.7 parts by weight of water, 0.1 parts by weight of COATSIDE H, 0.1parts by weight of PROXEL XL-2 and 15 parts by weight of saidwater-soluble resin liquid (20 wt % of styrene-acrylic acid resin, 2 wt% of caustic soda, and 78 wt % of water) were added, thereby obtaining awater base pigment ink.

Example 5

Inks with compositions shown in Table 1 were prepared respectively.

First, 25 parts by weight of phthalocyanine blue pigments, 20 parts byweight of ethylene glycol, 2 parts by weight of butylceilsolve, and 28parts by weight of water were added to 25 parts by weight of watersoluble resin liquid (20 wt % of styrene-acrylic acid resin, 2 wt % ofcaustic soda, and 78 wt % of water), followed by dispersing by apublicly known bead mill and further adding 32 parts by weight of waterso that pigments concentration gets 17 wt %, thereby obtaining waterbase pigment dispersion E.

Next, to this water base pigment dispersion E, with the content shown inTable 1, 28 parts by weight of glycerin, 10 parts by weight of urea,43.0 parts by weight of water, 0.1 parts by weight of COATSIDE H, 0.1parts by weight of PROXEL XL-2 and 15 parts by weight of saidwater-soluble resin liquid (20 wt % of styrene-acrylic acid resin, 2 wt% of caustic soda, and 78 wt % of water) were added, thereby obtaining awater base pigment ink.

Comparative Example 1

Inks with compositions shown in Table 1 were prepared respectively.

First, 25 parts by weight of azo yellow pigments, 20 parts by weight ofethylene glycol, 2 parts by weight of butylcellsolve, and 28 parts byweight of water were added to 25 parts by weight of water soluble resinliquid (20 wt % of styrene-acrylic acid resin, 2 wt % of caustic soda,and 78 wt % of water), followed by dispersing by a publicly known beadmill and further adding 32 parts by weight of water so that pigmentsconcentration gets 17 wt %, thereby obtaining aqueous pigment dispersionA.

Next, to 29 parts by weight of this water base pigment dispersion A, 3.0parts by weight of titanium dioxide dispersion, 27 parts by weight ofglycerin, 10 parts by weight of urea, 28.8 parts by weight of water, 0.1parts by weight of COATSIDE H (manufactured by Takeda Pharmaceuticalcompany limited), 0.1 parts by weight of PROXEL XL-2 (manufactured byAvecia K.K.) as antiseptic mildew-proofing agents, and 5 parts by weightof said water-soluble resin liquid (20 wt % of styrene-acrylic acidresin, 2 wt % of caustic soda, and 78 wt % of water) were added, therebyobtaining a water base pigment ink.

Comparative Example 2

Inks with compositions shown in Table 1 were prepared respectively.

First, 25 parts by weight of azo yellow pigments, 20 parts by weight ofethylene glycol, 2 parts by weight of butylcellsolve, and 28 parts byweight of water were added to 25 parts by weight of water soluble resinliquid (20 wt % of styrene-acrylic acid resin, 2 wt % of caustic soda,and 78 wt % of water), followed by dispersing by a publicly known beadmill and further adding 32 parts by weight of water so that pigmentsconcentration gets 17 wt %, thereby obtaining aqueous pigment dispersionA.

Next, to this water base pigment dispersion A, 27 parts by weight ofglycerin, 10 parts by weight of urea, 33.8 parts by weight of water, 0.1parts by weight of COATSIDE H, 0.1 parts by weight of PROXEL XL-2 asantiseptic mildew-proofing agents, and 5 parts by weight of saidwater-soluble resin liquid (20 wt % of styrene-acrylic acid resin, 2 wt% of caustic soda, and 78 wt % of water) were added, thereby obtaining awater base pigment ink.

Comparative Example 3

Inks with compositions shown in Table 1 were prepared respectively.

First, 25 parts by weight of quinacridone red pigments, 20 parts byweight of ethylene glycol, 2 parts by weight of butylcellsolve, and 28parts by weight of water were added to 25 parts by weight of watersoluble resin liquid (20 wt % of styrene-acrylic acid resin, 2 wt % ofcaustic soda, and 78 wt % of water), followed by dispersing by apublicly known bead mill and further adding 32 parts by weight of waterso that pigments concentration gets 17 wt %, thereby obtaining aqueouspigment dispersion B.

Next, to this water base pigment dispersion B, 28 parts by weight ofglycerin, 10 parts by weight of urea, 56.5 parts by weight of water, 0.1parts by weight of COATSIDE H, 0.1 parts by weight of PROXEL XL-2 asantiseptic mildew-proofing agents, and 5 parts by weight of saidwater-soluble resin liquid (20 wt % of styrene-acrylic acid resin, 2 wt% of caustic soda, and 78 wt % of water) were added, thereby obtaining awater base pigment ink.

Comparative Example 4

Inks with compositions shown in Table 1 were prepared respectively.

First, 25 parts by weight of DPP red pigments, 20 parts by weight ofethylene glycol, 2 parts by weight of butylcellsolve, and 28 parts byweight of water were added to 25 parts by weight of water soluble resinliquid (20 wt % of styrene-acrylic acid resin, 2 wt % of caustic soda,and 78 wt % of water), followed by dispersing by a publicly known beadmill and further adding 32 parts by weight of water so that pigmentsconcentration gets 17 wt %, thereby obtaining aqueous pigment dispersionC.

Next, to this water base pigment dispersion C, 25 parts by weight ofglycerin, 10 parts by weight of urea, 56.0 parts by weight of water, 0.1parts by weight of COATSIDE H, 0.1 parts by weight of PROXEL XL-2 asantiseptic mildew-proofing agents, and 5 parts by weight of saidwater-soluble resin liquid (20 wt % of styrene-acrylic acid resin, 2 wt% of caustic soda, and 78 wt % of water) were added, thereby obtaining awater base pigment ink.

Comparative Example 5

Inks with compositions shown in Table 1 were prepared respectively.

First, 25 parts by weight of phthalocyanine green pigments, 20 parts byweight of ethylene glycol, 2 parts by weight of butylcellsolve, and 28parts by weight of water were added to 25 parts by weight of watersoluble resin liquid (20 wt % of styrene-acrylic acid resin, 2 wt % ofcaustic soda, and 78 wt % of water), followed by dispersing by apublicly known bead mill and further adding 32 parts by weight of waterso that pigments concentration gets 17 wt %, thereby obtaining aqueouspigment dispersion E.

Next, to this water base pigment dispersion D, 25 parts by weight ofglycerin, 10 parts by weight of urea, 56.7 parts by weight of water, 0.1parts by weight of COATSIDE H, 0.1 parts by weight of PROXEL XL-2 asantiseptic mildew-proofing agents, and 5 parts by weight of saidwater-soluble resin liquid (20 wt % of styrene-acrylic acid resin, 2 wt% of caustic soda, and 78 wt % of water) were added, thereby obtaining awater base pigment ink.

Comparative Example 6

Inks with compositions shown in Table 1 were prepared respectively.

First, 25 parts by weight of phthalocyanine blue pigments, 20 parts byweight of ethylene glycol, 2 parts by weight of butylceilsolve, and 28parts by weight of water were added to 25 parts by weight of watersoluble resin liquid (20 wt % of styrene-acrylic acid resin, 2 wt % ofcaustic soda, and 78 wt % of water), followed by dispersing by apublicly known bead mill and further adding 32 parts by weight of waterso that pigments concentration gets 17 wt %, thereby obtaining aqueouspigment dispersion E.

Next, to this water base pigment dispersion E, 28 parts by weight of 5glycerin, 10 parts by weight of urea, 58.0 parts by weight of water, 0.1parts by weight of COATSIDE H, 0.1 parts by weight of PROXEL XL-2 asantiseptic mildew-proofing agents, and 5 parts by weight of saidwater-soluble resin liquid (20 wt % of styrene-acrylic acid resin, 2 wt% of caustic soda, and 78 wt % of water) were added, thereby obtaining awater base pigment ink.

TABLE 1 (wt %) Example Comparative Example 1 2 3 4 5 1 2 3 4 5 6 PigmentPigment dispersion A 30.0 30.0 30.0 Pigment dispersion B 5.8 5.8 Pigmentdispersion C 8.8 8.8 Pigment dispersion D 8.1 8.1 Pigment dispersion E3.8 3.8 Titanium dioxide 3.0 Dispersion¹⁾ Pigment concentration²⁾ 4.91.0 1.5 1.4 0.6 5.4 4.9 1.0 1.5 1.4 0.6 Water - soluble resin³⁾ 1.0 0.20.3 0.3 0.1 1.1 1.0 0.2 0.3 0.3 0.1 PROXEL XL-2 0.1 0.1 0.1 0.1 0.1 0.10.1 0.1 0.1 0.1 0.1 COATSIDE H 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.10.1 Resin in aqueous solution 5.0 15.0 15.0 15.0 15.0 15.0 (watersoluble resin⁴⁾) (1.0) (3.0) (3.0) (3.0) (3.0) (1.0) Glycerin 27.0 28.025.0 25.0 28.0 27.0 27.0 28.0 25.0 25.0 28.0 Water 27.8 41.0 41.0 41.041.7 43.0 24.8 32.8 56.0 56.0 58.0 Urea 10.0 10.0 10.0 10.0 10.0 10.010.0 10.0 10.0 10.0 10.0 Total (wt %) 100.0 100.0 100.0 100.0 100.0100.0 100.0 100.0 100.0 100.0 100.0 Total amount of water- 2.0 3.2 3.33.3 3.1 2.1 1.0 0.2 0.3 0.3 0.1 soluble resin(wt %) Evaluation Viscosity5.8 4.5 4.3 4.2 4.3 6.0 4.9 3.2 3.0 2.9 3.0 Concentration change in ⊚ ⊚⊚ ⊚ ⊚ X Δ X X X X erected/inverted state writing⁵⁾ (Note) ¹⁾titaniumdioxide dispersion: the dispersion is composed of 25 parts by weight ofwater-soluble resin, with 25 parts by weight of titanium dioxide, 20parts by weight of ethylene glycol, 30 parts by weight of water added,followed by dispersing with a publicly known bead mill and adding 32parts by weight of water so that concentration of titanium dioxide is 17wt %. In addition, water-soluble resin liquid is composed of 20 wt % ofstyrene acryl acid resin, 2 wt % of caustic soda, and 78 wt % of waterand water-soluble resin is a styrene acryl acid resin. ²⁾pigmentconcentration: pigment concentration with respect to the total amount ofthe ink (wt %) ³⁾water-soluble resin: styrene acrylic acid resinincluded in pigment dispersions A to E and concentration with respect tothe total amount of the ink (wt %) ⁴⁾water-soluble resin: styreneacrylic acid resin and concentration with respect to the total amount ofthe ink (wt %) ⁵⁾handwriting on paper and the concentration (wt %) ofwritten marks before and after storage visually observed ⊚ shows noconcentration change. ◯ shows substantially no concentration change. Δshows clear concentration change. X shows remarkable concentrationchange.

Pigment component as mentioned above shown in Examples and ComparativeExamples are as follows:

(Pigments)

Quinacridone (trade name: Chromophthal Pink PT manufactured by ChibaSpecialty Chemicals Co., Ltd.)

Phthalocyanine blue (trade name: Fastgen Blue TGR manufactured byDAINIPPON INK AND CHEMICALS INCORPORATED.)

Phthalocyanine green (trade name: Fastgen Green B manufactured byDAINIPPON INK AND CHEMICALS INCORPORATED.)

Azo yellow (trade name: Rheonol Yellow 10 GPT, manufactured by TOYO INKMFG. CO., LTD.)

DPP red (trade name: Chromophthal Red 2030 manufactured by ChibaSpecialty Chemicals Co., Ltd.)

(Evaluation of Ink Compositions)

Water base ink compositions obtained in Examples 1 to 5 and ComparativeExamples 1 to 5 were filled in inner lead type writing instruments andwritten marks were observed by writing on a paper sheet. Further, afterwriting, the writing instruments were left to stand under a temperatureof 50° C. for one month in erected state (state in which a pen tip isdirected upward) and in inverted state (state in which a pen tip isdirected downward), respectively, followed by writing and concentrationchange was compared with an initial state. The result is shown in Table1.

(Color Difference Between Writing Lines and White Paper)

Inks of Examples were written on white paper and color differencebetween the writing lines and white paper was evaluated. As ameasurement device, a color-difference meter with a trade name “CR-241”manufactured by KONICA MINOLTA Co., Ltd. was used and color differencewas measured based on JIS Z 8729 standard. As a result, while L* was93.8, a* 0.6, and b* −1.1 in white paper, L* is not less than 68 in inksof each Example, and color difference

E *(ab) between white paper was not greater than 45. By this, inks ineach Example were observed to have great degree of color development aspastel colors.

(Evaluation Result)

In water base ink compositions in Examples 1 to 5, pastel toned writtenmarks were obtained and there was no concentration change in erectedstates and inverted states and in writing characteristics. On the otherhand, although in water base ink compositions in Comparative Examples 1to 5, although pastel toned written marks were obtained, concentrationchange in erected and inverted states as well as writing characteristicswere remarkably bad.

As heretofore mentioned, a water base pigment ink composition for innerlead type writing instruments, by not using white colored pigments andby preparing specific content amount of pigments, by preparing specificcontent amount of water-soluble resin, and by setting specific inkviscosity, pastel-toned color can be obtained and when used for innerlead type writing instruments, dispersion stability of inks are obtainedand effects of preventing ink droplets and color shadings due to erectstates and inverted states of writing instruments. Further, ink leakageis not liable to occur from writing instrument containers.

INDUSTRIAL APPLICABILITY

Ink compositions of the present invention can be applied for inner leadtype writing instruments provided with publicly known structures. Forexample, such writing instruments have inner leads in which fiberbundles as ink containers are bundled and have pen tips which dischargeinks stored in inner leads, and as pen tips, for example, balls, fibers,plastic leads, brush-like materials, and pen-shaped materials areprovided.

1. Inner lead type writing instruments comprising: inner leads in which fiber bundles are bundled as ink containers and pen tips that discharge inks contained in said inner leads and are composed of any one of fibers, plastic leads, brush-like materials and pen-shaped materials, wherein said inks do not comprise white colored inorganic pigments or white colored resin particles as coloring materials, and the content of pigments other than said white colored inorganic pigments or white colored resin particles is 0.5 to 7 wt %, the content of water-soluble resin is 2 to 10 wt % with respect to the total amount of the ink, and the viscosity is 3.5 to 10 mPa·s.
 2. Inner lead type writing instruments comprising: inner leads in which fiber bundles are bundled as ink containers and pen tips that discharge inks contained in said inner leads and are composed of any one of fibers, plastic leads, brush-like materials and pen-shaped materials, wherein said inks do not comprise white colored inorganic pigments or white colored resin particles as coloring materials, pigments other than said white colored inorganic pigments or white colored resin particles are one or more species selected from quinacridone red, DPP red, phthalocyanine blue, phthalocyanine green, azo yellow, and disazo yellow, said water-soluble resins are one or more species selected from acrylic acid resins, styrene-acrylic acid resins, styrene-maleic acid resins, and the content of pigments other than said white colored inorganic pigments or white colored resin particles is 0.5 to 7 wt %, said water-soluble resin is 2 to 10 wt % with respect to the total amount of the ink, and the viscosity is 3.5 to 10 mPa·s. 